Deputy Foreign Minister Oleg Syromolotov said in an interview with the Tass news agency that several terror groups in western Siberia had stockpiled weapons for the attack. Twenty people have been detained and 17 homes were searched as part of the investigation, he said.

The announcement came as Russia prepares to host the World Cup next month.

Russia’s top intelligence agency last month reported the arrests of men suspected to have links to the Islamic State group in Siberia and the Moscow region.

A flypast during the mass rally (Pavel Golovkin/AP)

The FSB agency said four members of the suspected IS “sleeper cell” were detained in the Moscow region after they travelled from Novy Urengoi, an oil town in western Siberia. The FSB said they plotted attacks in Moscow and were receiving orders from IS members in Syria via a messaging app.

Oil and gas-rich western Siberia has for decades attracted workers from all over Russia, including the predominantly Muslim North Caucasus.

Russia has been providing air cover for Syrian President Bashar Assad since 2015, while thousands of its own citizens went to Syria to join IS in fighting against Assad’s government.